What is the difference between duration, work, effort, hours, and man-days?

I come from the Microsoft Project world where schedules are built using duration and work. However, ever so often team members refer to effort, hours, or my personal pet peeve “man-days”. What are all of these and how do they compare?

My nonprofessional definitions are summarized as follows, with examples below:

Duration – the amount of time it takes to complete a task. Measured in days, from task start to task end. Can also be referred to as calendar time.

Work – the amount of hours it takes to complete a task. Measured in hours, from task start to task end.

Effort – the same as work if you’re talking about hours. Technically, effort is a % allocation of your “focus” on a task.

Hours – the same as work.

Man-days – the same as work, but expressed in days instead of hours.

To illustrate, we will use a simple example: We need to build a wall.

Example 1: Duration

The wall will take one builder 10 working days to build. In Microsoft Project, this would be represented as follows:

Man-days is 10 days. Be careful! Man-days is not the same as duration. See the next example.

Example 2: Man-days

The same wall will take two builders 5 working days to build.

Duration is 5 days

Work is still 80 hours (2 builders, each working 8 hours a day for 5 days)

Effort is 80 hours

Hours is 80 hours

Man-days is 10 days

Example 3:

We have two builders, but the client will only allow us to work for 4 hours in the mornings. Thereafter, we need to leave the building site. The same wall will take the two builders 10 working days to build.

Duration is 10 days

Work is still 80 hours (2 builders, each working 4 hours a day for 10 days)

Effort is 80 hours

Hours is 80 hours

Man-days is 10 days

In Summary:

When team members start using non-standard terminology, make sure that you understand exactly what they mean. When quoting customers on a time and materials basis, work is the only reliable source in the examples above, work remained at 80 hours regardless of how the work was resourced. Wherever possible, I always refer to Duration and Work. These are two “standards” that most other Microsoft Project users will be familiar with. Leave a comment and let me know if you found this useful.